An acoustic shadow is an area through which sound waves fail to propagate, due to topographical obstructions or disruption of the waves via phenomena such as wind currents. A gobo refers to a movable acoustic isolation panel and that makes an acoustic shadow. As one website refers to it, "an acoustic shadow is to sound what a mirage is to light"[1].For example, at the Battle of Iuka, a northerly wind prevented General Ulysses S. Grant from hearing the sounds of battle and sending more troops. Many other instances of acoustic shadowing were prevalent during the American Civil War, including the Battles of Gaines' Mill and Perryville. (Also Seven Pines.)
Further reading
Garrison Jr., Webb, Strange Battles of the Civil War, Cumberland House, 2001, ISBN 1-581-82226-X
